On Thu, Sep 17, 2020 at 8:26 AM Sultan Alsawaf <sultan@xxxxxxxxxxxxxxx> wrote: > > From: Sultan Alsawaf <sultan@xxxxxxxxxxxxxxx> > > This is a fixed resubmission of "[PATCH 0/2] i2c-hid: Save power by reducing i2c > xfers with block reads". That original patchset did not have enough fixes for > the designware i2c adapter's I2C_M_RECV_LEN feature, which is documented > extensively in the original email thread. > > Here is the original cover letter, which still applies: > "I noticed on my Dell Precision 15 5540 with an i9-9880H that simply putting my > finger on the touchpad would increase my system's power consumption by 4W, which > is quite considerable. Resting my finger on the touchpad would generate roughly > 4000 i2c irqs per second, or roughly 20 i2c irqs per touchpad irq. > > Upon closer inspection, I noticed that the i2c-hid driver would always transfer > the maximum report size over i2c (which is 60 bytes for my touchpad), but all of > my touchpad's normal touch events are only 32 bytes long according to the length > byte contained in the buffer sequence. > > Therefore, I was able to save about 2W of power by passing the I2C_M_RECV_LEN > flag in i2c-hid, which says to look for the payload length in the first byte of > the transfer buffer and adjust the i2c transaction accordingly. The only problem > though is that my i2c controller's driver allows bytes other than the first one > to be used to retrieve the payload length, which is incorrect according to the > SMBus spec, and would break my i2c-hid change since not *all* of the reports > from my touchpad are conforming SMBus block reads. > > This patchset fixes the I2C_M_RECV_LEN behavior in the designware i2c driver and > modifies i2c-hid to use I2C_M_RECV_LEN to save quite a bit of power. Even if the > peripheral controlled by i2c-hid doesn't support block reads, the i2c controller > drivers should cope with this and proceed with the i2c transfer using the > original requested length." Reviewed-by: Andy Shevchenko <andy.shevchenko@xxxxxxxxx> for I²C DesignWare patches. > > Sultan > > Sultan Alsawaf (4): > i2c: designware: Fix transfer failures for invalid SMBus block reads > i2c: designware: Ensure tx_buf_len is nonzero for SMBus block reads > i2c: designware: Allow SMBus block reads up to 255 bytes in length > HID: i2c-hid: Use block reads when possible to save power > > drivers/hid/i2c-hid/i2c-hid-core.c | 5 ++++- > drivers/i2c/busses/i2c-designware-master.c | 15 +++++++++------ > 2 files changed, 13 insertions(+), 7 deletions(-) > > -- > 2.28.0 > -- With Best Regards, Andy Shevchenko
